DEVELOPMENT OF PREFERENCE AND SPONTANEOUS-RECOVERY IN CHOICE BEHAVIORWITH CONCURRENT VARIABLE-INTERVAL SCHEDULES

Pigeons pecked on two response keys that delivered reinforcers on a va riable-interval schedule. The proportion of reinforcers delivered by o ne key was constant for a few sessions and then changed, and subjects' choice responses were recorded during these periods of transition. In Experiment 1, response proportions approached a new asymptote slightl y more slowly when the switch in reinforcement proportions was more ex treme. In Experiment 2, slightly faster transitions were found with hi gher overall rates of reinforcement. The results from the first sessio n, after a switch in the reinforcement proportions, were generally con sistent with a mathematical model that assumes that the strength of ea ch response is increased by reinforcement and decreased by nonreinforc ement. However, neither this model nor other similar models; predicted the ''spontaneous recovery'' observed in later sessions: At the start of these sessions, response proportions reverted toward their preswit ch levels. Computer simulations could mimic the spontaneous recovery b y assuming that subjects store separate representations of response st rength for each session, which are averaged at the start of each new s ession.